Separation of high and low quality electrode cokes



May 9, 1967 J. ELLINGBOE, JR, ET AL 3,318,447

d Feb. 5, 1964 LLLLLLLLLLLLLLLL R.

United States Patent 3,318,447 SEPARATION OF HIGH AND LOW QUALITY ELECTRODE COKES John L. Ellingboe, Jr., Littleton, and John H. Runnels, Denver, Colo., assignors to Marathon Oil Company, Findlay, Ohio, a corporation of Ohio Filed Feb. 3, 1964. Ser. No. 341,976 4 Claims. (Cl. 209-213) The present invention relates to a method for producing petroleum coke having superior physical characteristics. More specifically, the present invention relates to the production of petroleum cokes having low or preselected coefiicients of thermal expansion.

Petroleum coke is the solid residue remaining after destructive distillation of petroleum materials. The fixed or solid carbon content is in the range of from about 90% to 95%. Because of its high purity, such coke is used extensively in metallurgical processes. For example, one major application is in the manufacture of electrodes for use in the Hall process for the electrolytic production of aluminum and the electric furnace production of steel.

In producing electrodes from petroleum cokes, attention has been given to the selection of cokes having thermal expansion characteristics suiting them for use over a wide range of temperatures. In general, petroleum cokes having low coefficients of thermal expansion, i.e., less than about 30x10 and preferably less than about 6x10 are preferred and produce superior electrodes which are less susceptible to cracking due to the stresses introduced by operation at elevated temperatures.

Heretofore, the matter of coke selection has been a painstaking batch by batch process. Each sample of petroleum coke was analyzed. If it was within the desired range of values for coefiicient of thermal expansion, it was used to produce electrodes and if not, it was put to other economically less valuable uses, such as fuel.

We have now found that petroleum cokes having desirably low and pre-selected values for coeflicient of thermal expansion may be produced. The present invention comprises subjecting finely divided petroleum coke to a magnetic field to form a relatively paramagnetic fraction and a relatively diamagnetic fraction and then separating the resulting fractions. Underlying this invention is the discovery that petroleum coke contains fractions which are relatively paramagnetic and diamagnetic, that the fractions may be separated on this basis by subjecting the coke to a magnetic field and that the paramagnetic fraction characteristically has a lower coefiicient of thermal expansion than the diamagnetic fraction.

By means of our process, petroleum coke fractions having relatively low value coefficients of thermal expansion may be obtained from an initial mass of petroleum coke. Also, after obtaining a fractionhaving a low coefiicient of thermal expansion, this material may be blended with petroleum coke having a higher coefiicient of thermal expansion. The mixtures so produced may have any intermediate preselected coeificient of thermal expansion by controlling the proportions of each type of coke added to the mixture.

The present invention may be more fully appreciated in the light of the following detailed description of one method for practicing the invention. Reference to the accompanying drawing will also assist in reaching a more complete understanding of the principles involved.

In the drawing, the figure is a perspective, somewhat schematic view of an apparatus suitable for practicing the invention.

The present method by which petroleum coke is treated to obtain a fraction having a relatively low coetficient of thermal expansion may be modified in some particulars, but in general it comprises passing finely divided particles of petroleum coke through a magnetic field. The magnetic field intensity and location are controlled so that a paramagnetic fraction of the coke is attracted to and a diamagnetic fraction is repelled by the magnetic field.

A divider in the system may then be employed to segregate the attracted and repelled fractions so that they may be recovered separately.

Suitable apparatus for carrying out the present invention is somewhat schematically illustrated in the figure of the drawing. Other devices of this type are described in US. Patents 2,056,426, Frantz; 1,453,699, Brophy; and 1,512,870, Ullrich et al. Additionally, the coke particles can be separated while flowing slowly downwardly against an air stream.

In practicing the present invention, a starting mass of petroleum coke is first comminuted, for example to a particle size of approximately to mesh. The coke treated may be one with an unsuitably high coetficient of thermal expansion, generally about 30 10 but any petroleum coke may be treated in the same manner.

The process is well adapted to operation on a continuous basis, in which case, the rate .of feed of the coke is controlled so as to maintain a fairly constant coke level within sloping separation chamber 11. The comminuted coke is fed through feed pipe 10 into the chamber 11.

Magnet 12 is activated by passing electric current through coil 13 to generate a magnetic field within chamber 11 which attracts the paramagnetic particles 14 to wall 15 of the chamber. The relatively diamagnetic particles 16 continue to slide along wall 17 of conduit or chamber 11.

Divider 18, placed in the path of the coke, separates the coke into two streams, indicated by differing coarseness of the coke particles shown in the drawing. The stream carrying the paramagnetic particles is then removed through channel 19 into trough 20 and the stream carrying the diamagnetic particles is conducted into channel 21 and thence into trough 22. Vibrator 23 insures continuous flow of coke down chamber 11.

By applying a current of from about 0.8 to 2.0 amps to coil 13 in a device of the type illustrated, a magnetic field of from 11,000 to about 20,000 gauss is generated in chamber 11. As the magnetic field is increased from lower to higher values, the amount of coke recovered in the paramagnetic fraction decreases.

Example I Four samples of petroleum coke were passed through a S. G. Frantz Co., Inc., Isodynarnic Separator, at varying magnetic field strengths. The samples had original coefficients of thermal expansion (CTE), as calculated Diamagnetic Paramagnctic Sample No.

Percent GTE Percent CTE Example II Additional portions of 1, 2 and 3 of Example I and a fourth coke (numbered 5 in the table below) were passed through the separator of Example I at varying magnetic fields. The initial CTE, magnetic field strength, and resultant percentages of relatively paramagnetic and relatively diamagnetic cokes separated are set out in the following table.

MAGNETIC FIELD STREN GTH-COKE SEPARATION Magnetic Percent Recovery Coke Initial GTE Field, Sample XlO- Gauss H Diamagnetic Paramagnetrc Once a coke fraction having a low coefiicient of thermal expansion is obtained, it may be blended with various amounts of petroleum coke having a higher coefficient of thermal expansion to produce products of any desired intermediate value. For example, a 50:50 mixture of the paramagnetic fractions having coefficients of thermal expansion of 3 10- and 13x10 respectively will give a mixture having a coefiicient of 8X10 cm./cm./ C.

Accordingly, the present invention provides an eflicient low cost method for obtaining valuable petroleum coke products from masses of petroleum coke of less economic value. In particular, it permit-s the rapid recovery of petroleum coke having a low coefiicient of thermal expansion from starting coke materials having undesirably high coefficients of thermal expansion.

It will be obvious to those skilled in the art that the present invention may be modified in various particulars without departing from the essential spirit of the invention as defined in the following claims.

What is claimed is:

1. A method for recovering petroleum coke having a relatively lower coefficient of thermal expansion from an initial mass of petroleum coke comprising:

subjecting a continuous stream of finely divided particles of said initial mass of petroleum coke to a high intensity magnetic field, and

separating those particles of petroleum coke which are attracted by said magnetic field and which are characterized by a coefficient of thermal expansion which is lower than that of said initial mass of petroleum coke.

2. A method for recovering petroleum coke having a relatively lower coefficient of thermal expansion from an initial mass of petroleum coke comprising:

subjecting a continuous stream of finely divided particles of said initial mass of petroleum coke to a magnetic field having a strength of more than 15,000 gauss, and

separating those particles of petroleum coke which are attracted by said magnetic field and which are characterized by a coeflicient of thermal expansion which is lower than that of said initial mass of petroleum coke.

3. A method for recovering petroleum coke having a relatively lower coefiicient of thermal expansion from an initial mass of petroleum coke comprising:

subjecting a continuous stream of finely divided particles of said initial mass of petroleum coke to a magnetic field having a strength in the range of from 15,000 to 20,000 gauss, and

separating those particles of petroleum coke which are attracted by said magnetic field and which are characterized by a coefiicient of thermal expansion which is lower than that of said initial mass of petroleum coke.

4. A method for recovering petroleum coke having a relatively lower coefiicient of thermal expansion from an initial mass of petroleum coke comprising:

feeding a substantially continuous stream of finely divided particles of said initial mass of petroleum coke downwardly under gravity through an inclined conduit,

subjecting the particles in said conduit to a magnetic field having a strength in the range of from 15,000 to 20,000 gauss, so that the relatively paramagnetic fraction of the particles in the stream is attracted to one wall of said conduit, and

separating the relatively paramagnetic particles of said petroleum coke which are characterized by a coefiicient of thermal expansion which is lower than that of said initial mass of petroleum coke;

References Cited by the Examiner UNITED STATES PATENTS 653,342 7/1900 Gates 209-212 1,071,838 9/ 1913 Weatherby 209-214 1,956,760 5/1934 Forrer 209223 2,056,426 10/ 1936 Frantz 2094-214 X 2,065,460 12/1936 Johnson 209-2l4 3,006,472 10/1961 Clute 209-214 FOREIGN PATENTS 1,061,714 7/1959 Germany.

HARRY B. THORNTON, Primary Examine R. HALPER, Assistant Examiner. 

1. A METHOD FOR RECOVERING PETROLEUM COKE HAVING A RELATIVELY LOWER COEFFICIENT OF THERMAL EXPANSION FROM AN INITIAL MASS OF PETROLEUM COKE COMPRISING: SUBJECTING A CONTINUOUS STREAM OF FINELY DIVIDED PARTICLES OF SAID INITIAL MASS OF PETROLEUM COKE TO A HIGH INTENSITY MAGNETIC FIELD, AND SEPARATING THOSE PARTICLES OF PETROLEUM COKE WHICH ARE ATTRACTED BY SAID MAGNETIC FIELD AND WHICH ARE CHAR- 